If someone has been taking dogs out of back yards and unleashing them then wouldn't it be very unsafe to leave your dog alone outside?

You could get a dog run with a roof, so the dog can't jump out. Something like this. And you could put a lock on it too, if you think someone might steal her while she's outside.

I don't know though, it sounds like maybe you should lock your doors if someone is letting dogs loose though. I know if that happened in my neighborhood I'd be scared for my dog.